The present invention relates to a rolling bearing for devices that are required to operate at a high temperature and a high velocity such as automobile alternator. More particularly, the present invention relates to a rolling bearing comprising a retainer having a heat resistance, oil resistance and high-velocity durability.
In general, rolling bearings can be divided into two groups, i.e., ball bearing and roller bearing, by the kind of rolling element to be incorporated therein. These ball bearings and roller bearings can be divided into several kinds by their shape and purpose. Accordingly, there are various kinds of retainers for use in these bearings.
In general, a ball bearing is often provided with a crown retainer 6 shown in FIG. 1. For example, a rolling bearing having the crown retainer shown in FIG. 1 mounted thereon comprises an inner ring 2 having a raceway 1 on the periphery thereof, an outer ring 4 having a raceway 3 on the inner surface thereof, a plurality of rolling elements 5 provided interposed between the inner ring 2 and the outer ring 4, and a crown retainer 6 provided rotatably between the inner ring raceway 1 and the outer ring raceway 3 for supporting and guiding the plurality of rolling elements 5, as shown in FIG. 2.
Examples of this type of a retainer include metallic retainer, and plastic retainer. As the material constituting the plastic retainer there has heretofore been used a so-called engineering plastic such as polyamide, polyacetal, polybutylene terephthalate and fluororesin, singly or in composite form obtained by reinforcing with a short fiber such as glass fiber and carbon fiber. Among these materials, polyamide has well-balanced material cost and performance and thus has been widely used as a material constituting the plastic retainer. It has been confirmed that plastic retainers made of polyamide exhibits an excellent performance.
However, polyamide 6 (nylon 6) and polyamide 66 (nylon 66), which have heretofore been commonly used as polyamide, are disadvantageous in that they are subject to deterioration with time under continuous working conditions at an ambient temperature of not lower than 120° C. or under conditions such that they come into continuous or intermittent contact with oils such as extreme pressure additive and additive oil and thus cannot satisfy the requirements of the market.
In recent years, improvements for energy saving have been under way in automobile industry. For example, it has been heretofore usual that alternators are air-cooled by cooling fan in operation. However, the trend is for more alternators to be water-cooled for the purpose of enhancing efficiency. Under these circumstances, the rolling bearings for use in these alternators have been more subject to high temperature than every and thus have been required to withstand higher temperatures.
Further, when used under working conditions such as high temperature and high rotary speed (e.g., 20,000 rpm), retainers made of conventional polyamides exhibit an insufficient heat resistance and insufficient high temperature strength and rigidity that cause deformation during rotation, resulting in contact with the outer ring of the bearing and hence abrasion on the retainer or seizing on the bearing. This, too, makes it impossible for these retainers to satisfy the requirements of the market.
Under these circumstances, as a material constituting the plastic retainer to be used at an ambient temperature as high as higher than 150° C. there has recently been proposed a so-called superengineering plastic resin such as polyether sulfone (PES), polyetherimide (PEI), polyamidimide (PAI) and polyimide (PI).
However, despite their excellence in heat resistance and chemical resistance, these proposed materials are disadvantageous in that they leave something to be desired in flexibility necessary for retainer, making it difficult for the resulting retainer to be assembled into bearing. Accordingly, these materials have never been widely used.